"Lew welcomed China's recent announcement to widen the daily trading band for the renminbi against the U.S. dollar and emphasized the need for China to move towards a market-determined exchange rate," the spokesperson said.

China's central bank eased its grip on the yuan on Saturday by doubling the daily trading range for the currency. The move added teeth to a promise it would allow market forces to play a greater role in the economy and its markets.

The People's Bank of China (PBOC) said the exchange rate will be allowed to rise or fall 2 percent from a daily midpoint rate CNY=SAEC it sets each morning. The change is effective from Monday.

Analysts said the move was a sign of confidence that the central bank had successfully fought off a plague of currency speculators and signaled that regulators believe the economy was stable enough to handle more promised reforms going forward.